1. Field of the Invention
This invention relates to a heavy duty pneumatic radial tire for use in truck, bus and the like comprising a bead portion provided with a wire chafer having an outer end positioned outward over an outer end of a turnup portion of a carcass ply in a radial direction of the tire. More particularly it relates to a heavy duty pneumatic radial tire effectively enhancing cornering power to improve a cornering property.
2. Description of Related Art
For example, the heavy duty pneumatic radial tire for use in truck, bus and the like generally has such a structure that a carcass ply is toroidally extended between a pair of bead cores and each end portion thereof is turned up around the bead core from inside toward outside. A tread portion is reinforced by plural belt layers and is superimposed about an outer periphery of a crown portion of the carcass ply. A wire chafer or the like for reinforcing the bead portion is arranged on an outer surface of a turnup portion of the carcass ply.
In case of the tire comprising the bead portion provided with the wire chafer, in order to prevent separation failure at the end of the turnup portion of the carcass ply, the wire chafer is arranged to cover the end of the turnup portion, or the wire chafer is frequently arranged so that the outer end of the wire chafer is located outward over the outer end of the turnup portion in the radial direction of the tire.
However, when the outer end of the wire chafer is arranged to locate outward from the outer end of the turnup portion in the radial direction of the tire, as a turnup length of the turnup portion of the carcass ply is relatively short, a length of a wire cord embedded in the turnup portion is apt to become shorter, so that the bending rigidity of the bead portion at in section thereof is not sufficiently obtained and the falling-down of the bead portion becomes larger during the running of the tire under loading and as a result, the cornering property tends to be degraded.
As means for enhancing the bending rigidity, it is useful to newly establish, for example, a wire chafer or a nylon chafer, or to use a stiffener having a high hardness or the like, but it is difficult to effectively enhance the bending rigidity by only these means.